If you aim to see that the city and surroundings, then this trip will be interesting to a child older than 6-7 years. At this age, they are starting to better perceive the beauty of the usual things, hardier in campaigns around the city. And in St. Petersburg will have to walk a lot, otherwise you risk to miss all the fun.
If you are coming for a couple of days, it is better to stay at a hotel in the city itself. If you come a week or two, then look for country hotels. So you and admire the beauty of the city, and breathe in the sea air.
To ensure that the child is not tired, you need to think about the day's program so that each family member were interesting activities. For the first half of the day, plan a visit to estates or museums, and in the evening you can take a relaxing walk along Nevsky, go by boat, sit in a restaurant.
Combine fun with a cultural program. For example, in the morning you can walk to the Hermitage. On weekdays, there is a small line at the cashier. And then go to the amusement park. If the weather is good - it can be an open-air park - Divo island. And if the weather is the real St. Petersburg, with rain - indoor amusement park pirate Happylon. Be sure to visit the aquarium, it will be interesting to children and adults of all ages.
Move to distant places of the city and its surroundings better on water transport. By boat and you can get to Peterhof and Kronstadt. And, of course, a ride on the canals. This tour will see the entire architecture of the city, hidden behind the facades of buildings. Just keep in mind that during the cold this trip with a baby is not desirable - from the Gulf of blowing very cold wind.
Trip to Peterhof can take a whole day, but that day can not be called lost. The palace itself can not watch if the child is already tired of museums, and in turn, there is a very large, especially on weekends. But the park with its magnificent fountains interest of even the most capricious child.
Be sure to visit the Church of the Savior on Spilled Blood. There is a constant tour, and you can at any time be attached to the group. The guide tells about the history of the construction of the temple, his fate and artistic decoration of the church receptions. The story is interesting, dynamic and child will not be bored.